This invention relates to alarms for emergency vehicles or the like, and more particularly to a low frequency cutoff for a voltage controlled oscillator (VCO) in a siren.
It can happen in a siren system that an input oscillator (IO) used to drive a VCO has an input lead which can be grounded for actuation of the IO. Further, the IO input lead rises in potential when disconnected from ground. Still further, together, the IO and VCO can drive a speaker in an output circuit at lower than normal operating frequencies when the IO input rises. When so driven, the speaker can become damaged. This is true because the IO output can, when the IO is shut off, fall below its normal and actuated operating range.